XML World File Format at a Glance

This article intends to breakdown the Initialisation Section of the CS world file into it's different parts in-order to explain syntax and common usage although much of this is covered in the documentation some parts are not up to date and often aren't explained properly so this article hopes to pick up where the documentation leaves of so to speak.

First of all, because the CS world format has the advantage of being in an ACSII format we can open in up in a standard text editor preferably one with XML syntax highlighting for simplification. So either start a new document or open an existing world file for editing (many examples can be found in the CS/data/ sub-directories)

In the beginning...

All CS world File must start with the <world> tag and end with </world>. So to start us off we'll have:

<world>
</world>

Note that if you want to make a library then just replace world with library. The rest of this tutorial is also valid for libraries except that libraries can only contain textures, materials, and mesh factories and no sectors.

Adding a Texture

Next we initialise which textures and materials we intend to use this is done by specifying VFS paths. VFS paths are a way of defining real paths without using Operating-System specific functions, so you must mount the directories that your textures are in on the VFS in order for them to be found.
VFS (Virtual File System) paths in case you were wondering are not just ordinary file system paths but paths that CS has set to ensure multi-platform compatibility, real paths are usually mounted to VFS paths in the vfs.cfg for example /lib/stdtex is actually a zip file called stdtex.zip in CS/Data which has been mounted to /lib/ VFS path, this comes in handy as you can refer to zip files as folders just by mounting them. We start by specifying that we are talking about textures using the <textures> tag and then specify which texture we are using with the <texture> tag, and specify it's location using the <file> tag.

This would apply the shader, but if we were to examine the actual shader we would notice that it also takes 2 variables which we can specify here. One is a texture that will be overlayed on the existing texture, and the other is a 2-D vector which basically shrinks down that texture to that scale.
To use these variables we would do the following:

Luckily for us this shader is a standard shader and the default renderloop already includes standard shaders, had this been another kind of shader we would have needed to change the renderloop. I decided to keep the same texture as the detail texture to avoid having to specify another texture and shrunk it by 10 UV's. If you are confused as to how i got the variable names and types, you can check cs/data/shaders/std_lighting_detail.xml for the type and names of the shader variables it takes. This is the same for all shaders.

So Far

So far we have specified a simple texture, material and shader-setup which looks like this:

Addings Sounds

Adding A Library

Another way of defining almost all of these things, is the use of libraries. A library is structured very much like a world file only it starts with <library> and ends in </library> it also cannot accept start locations and sectors. It is a good way of grouping certain things for loading. Also if specifying mesh factories in a library you will be able to load them into viewmesh. To include a library in a world file we would use:

<library path="/lib/std" file="library" />

Adding Plugins

There are an array of plugins that need to be handled in CS, only including the ones you need is the best way to go about things.For this reason we shall only include the thing-loader and factory plugin for this example.

We do this to allow us to use the full potential of it's factory and mesh setup.
Thing meshes are usually low-poly meshes that use pre-calculated light-mapped surfaces. Their downside is that they are less efficient than a general mesh.

Adding Settings

Settings are there to over-ride some default engine settings such as ambient light and lightmap size you can read about them in the documentation.

Adding Factories

The Factory/meshobject scenario is often important if you wish to repeat meshes several times. But not always necessary if you wish to just have one instance of a mesh. For this article I will be taking advantage of the Factory/Meshobject setup to better familiarize users with it.

In a factory we usually tell the engine what factory will be called, the plugin used, the geometry information and also material(s) used on the mesh. With a thing mesh we have the option of mutliple materials based on the polygons you assign it to. This factory was taken from the simple map tutorial in the documentation. It is a simple cube with a single material applied.

The first line initilises and names the meshfactory. The second tells the loader what plugin we are using in this case a thing factory becuase we are defining geometry. <zfill /> is used so that the card ignores the zbuffer and draws the Z value from the thing polygons over the old Z values present on screen. This is used by the outermost walls because it is a faster mode than <zuse/> as it does not need to read the zbuffer. It will be the first thing rendered in a back2front render. The next block is actually defining the position of vertexes. This box is made up of 8 vertexes. Next is the material. We specify the material we created earlier (old metal). Now we set <texlen> to 4 meaning that for every 4*4 world units one texture will be tiled. Next we define polygons by specifying the vertices that make up that polygon but remember that vertices start to count at 0. These polygons can also have names for debugging reasons mostly but they can have other uses.

And that brings a close to our initialisation section of a world file. In the rest of this tutorial I will tell you how to use these to create a sector in a world that can be loaded by walktest.

Creating a Room

Starting Us Off

Now is time for use to use those loaded resources and create a simple room runable in walktest. Now normally the definition section would probly be the largest part of the world file, luckily we only have a small amount of objects. To Start us of, no pun intended we need a Spawning position we specify it like this:

<start>
<sector>room</sector>
<position x="0" y="0" z="0" />
</start>

"room" will be the eventual name of our sector. 0,0,0 will be the coordinate in that sector in which we shall spawn (Crystal Space Does not actually care about this, it is very app-specifc the way you handle start points. You can have multiple start positions and have people spawn at different locations). Now we create and name our sector like so:

Creating a Sector

<sector name="room">
</sector>

Adding our MeshObj from a Factory:

We now have a sector called room which we can fill with whatever we want and the first thing we shall fill it with will be our Thing Factory called walls, here is how we do it:

As you can see we once again name the mesh this is because we need to distinguish between mesh objects sharing the same factory in case we use that factory more than once. The second line that has been added is refering to the loader plugin, do not confuse this with the factory plugin if you look at the <plugin> section we have initialised two plugins: the loaded and factory.
The <params> sections only needs to have a reference to our factory. If I had not used a factory this would be the section where I would place the vertex and polygon information along with the materials. And finaly we terminate our meshobj section and we're done with this part.

Adding A Light

At this point if we were to load the world file with this into walktest it would work, But you would not be able to see anything. why you ask? No lights. To add a light we have the following:

We should be able to see from this that it is named "light1" and it will be created where we spawn (0,0,0 in sector "room"). Also i've set its radius to 20. This does not mean that everything will be full bright. It only means that the light will not begin to falloff as soon. Also light values are worked out on a percentage for colours r1g1b1 (100% Red 100% Green 100% Blue) being white but also the larger numbers have greater intensity meaning this is 2x brighter than a r1g1b1 light. The Last line is preperation for the final part of this series where we will manipulate the light's colour.

Loading Your Level Into Walktest

This level is now ready (syntax wise) for walktest. To actually run it you have to specify the directory where the world file is located to walktest like this:

walktest directory_for_world

If you put world in the current directory then you can also do:

walktest /this

The reason this all works is that walktest accepts both VFS paths (the /this above) and normal paths (the directory_for_world). The VFS path /this is very useful for debugging (but should otherwise be avoided) and refers to the current directory.

Sectors And Portals

It seems that other articles have shed away from dealing with sectors and portals, so i decided to add another sector to this tutorial.

Duplicating your Sector

Currently room2 is just a duplcate of room, what we want is another room on the side of room, to do this we must translate out light and walls 20 units in a direction, i chose the positive X direction. To do this we add a <move> tag to our mesh object like this:

Note that we also moved the light. We now have two rooms side by side, Unfortunately they are not connected at all. I did not have to separate these into seperate sectors but a constricted doorway is a good opportunity to take advantage of portals and sectors. We are going to create a floating portal as not to distrub the geometry by adding a polygon inside the face, normally adding a portal polygon to a mesh would be a better solution as that way portals line up correctly with walls, but this portal is for illustrative purposes and concepts only.

Portals

To start off we'll place a portal from room to room2' because is a floating portal we will not need it nested in a meshobj so we start by adding this to the room sector (add this right before the light for example):

Once again we are not able to see the portal because our render-priorities are not currently set, meaning our zfill walls don't know they are ment to be behind our portal so for our special case we need to use the object priority like so:

Finally we are able to see our portal, unfortunately due to the nature and position of our portal it only warps us to the same position in the neighbouring sector, we need a bit of space warping and here's how we do it:

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Contrary to popular belive we will have to warp using negative coordinates if you wish to visualise this it is asif we are moving the world one unit toward the player.(unless of course we wanted to rotate our space in which case we would need a positive <wv /> coordinate and a rotation matrix)
The Last thing that is needed is the <float /> tag to indicate it is a floating portal and it is not on the boundary of a sector.
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And we're done, you should be able to load up you level (if you have been following) and get from room1 to room2 but not back again, i won't repeat the making of this portal I will just paste the portal code, all the same principles apply.
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